Field
Apparatuses and methods consistent with exemplary embodiments relate to a manipulator, and more particularly, to an articulated manipulator capable of moving a tool such as an inspection device, a processing device, or a welding device to a desired position for inspection or repair of a defect portion in a limited place.
Description of the Related Art
A steam generator constituting a nuclear steam supply system of a nuclear power plant is a device which generates dry steam when high-temperature primary coolant supplied from a reactor exchanges heat with secondary coolant outside heat transfer tubes while flowing along the heat transfer tubes inside the steam generator.
A primary system of a nuclear power plant is typically configured by a reactor, a steam generator, a coolant circulation pump, a pressurizer, and the like. Here, the reactor has a control rod and a fuel assembly therein, and heat energy generated in the reactor is transferred to the outside of the reactor through a primary coolant. The primary coolant is circulated through heat transfer tubes via the steam generator.
The steam generator is supplied with secondary coolant which exchanges heat with the primary coolant. The secondary coolant exchanges heat with the high-temperature and high-pressure primary coolant to be vaporized. Steam generated by the steam generator is transferred to a turbine through a pipe so as to drive a generator and generate electric energy.
FIG. 1 is a view illustrating an example of a typical steam generator.
Referring to FIG. 1, a steam generator 10 has a plurality of heat transfer tubes (several thousand or more heat transfer tubes) 11 therein, and a tube sheet 12 and a channel head 13 are formed at a lower portion of the steam generator 10.
An inner portion of the channel head 13 is partitioned by a partition plate 14, and an inlet 15 and an outlet 16 are formed on an outer peripheral surface of the channel head 13 so as to respectively communicate with spaces partitioned thereby.
Primary coolant discharged from a reactor is introduced into the inner space through the inlet 15 of the channel head 13, exchanges heat with secondary coolant through the heat transfer tubes 11 via the tube sheet 12, and is then discharged to the outlet 16. Accordingly, the tube sheet 12 is formed with through-holes (not shown) communicating with the respective heat transfer tubes 11.
A large number of defects due to corrosion or external impact tend to be generated at welding portions of the partition plate 14 after the steam generator 10 has been operated for a long time. Thus, the defects have to be inspected and repaired in order to prevent safety accidents.
In this case, the inspection and repair are mainly performed by mechanical devices which are remotely controlled from the outside, because of a danger of residual radioactivity and also because of the small space within the channel head 13. Therefore, there is a need for a manipulator capable of accurately locating an inspection device or a repair device at a defect portion in order to improve accuracy of inspection and repair.
FIG. 2 is a cross-sectional view illustrating various welding portions in the channel head.
As shown in FIG. 2, the channel head 13 is provided with welding portions which are respectively formed between the partition plate 14 and the channel head 13, between the partition plate 14 and the tube sheet 12, and between the partition plate 14 and a stub runner 17. The manipulator needs to move the inspection device or the repair device to various positions corresponding to the respective welding portions.
In addition, the inner space of the channel 13 is formed in various sizes according to the standard of the steam generator 10. Accordingly, in order for the manipulator to be applied to the various-sized work spaces, the number of rotary shafts of or shape of the manipulator needs to be actively changed and the shape of the manipulator has to be easily changed for improvement of workability.